Field
The present application relates to tunable lasers, optical amplifiers, and to optical communication systems.
Related Art
Tunable lasers conventionally consist of a tunable wavelength filter and a single optical gain medium inside a resonant laser cavity. A depiction of a conventional tunable laser 100 is shown in FIG. 1. The laser cavity may include an intracavity beam 102 that reflects between a high-reflector end-mirror 105 and partially-transmitting mirror 140 (referred to as an “output coupler”). The intracavity beam passes through the gain medium 110 and tunable wavelength filter 130 as it circulates between the end-mirror and output coupler.
Such lasers normally have only one output beam 104, which emits from the output coupler 140. For example, the output coupler may transmit about 10% of the optical power in the intracavity beam 102 outside the laser cavity to form the output beam 104. Conventionally, the amount of power coupled outside the laser cavity cannot be adjusted while the laser is operating. Instead, the laser must be shut off, and a different output coupler 130 installed and aligned.
Because a conventional laser contains one gain medium, the laser power is limited by the saturation power of the gain medium 130. Once the saturation power level is reached in the gain medium, no further substantial increase in output power from the laser cavity can be achieved. To increase available laser power, a conventional technique passes the output beam 104 through an optical amplifier located downstream of the laser 100.